The origin and the fate of the cranial ribs in the avian chondrocrania

The origin and the fate of the cranial ribs in three birds; Streptopelia senegalensis aegyptiaca, Pterocles alchata caudacutus and Passer domesticus niloticus, have been described. The requested characters for true cranial ribs are determined. The probable assumption that cranial ribs are developed in all birds is suggested, but because of their rapid regression several successive young stages are needed for their identification. The present finding invalidates De Beers & Barrington’s and Slaby’s theory that the metotic cartilage in birds originates from the cranial ribs.